I. Field of the Invention
The present invention relates to test fixtures for determining dielectric properties of a material, and more particularly, to such test fixtures for making such determinations at microwave frequencies.
II. Description of the Prior Art
By way of background, some known test fixtures for determining dielectric properties of a test material at microwave frequencies input microwave energy into one end of an electrical conductor at least partially surrounded by the test material and provide an output for that energy at another end of the surrounded conductor. From power measurements made of the microwave energy input to and output from the surrounded conductor, various dielectric properties of the surrounding test material may be determined.
One drawback with a typical test fixture is that measurement of the input microwave energy requires use of additional equipment such as directional couplers and standing wave reflection (SWR) meters. A further drawback to such a test fixture is the limited range of microwave frequencies over which testing can be obtained.
As is well understood, the input frequency of the microwave energy is varied to locate resonant spectral points and harmonics thereof. The -3 db, or half-power, points about these spectral points of interest are then recorded and used for determining the dielectric properties of the test material. The more spectral points of interest about which measurements can be taken, the more verifiable the dielectric determinations. In order to increase the input range of typical test fixtures, the test material may have to be removed to allow the test fixture to be altered structurally or even replaced. Such changes during testing degrade the reliability and repeatability of the dielectric determinations.